Recently, illuminating fixtures using a semiconductor light emitting element such as a light emitting diode (an LED), an organic electroluminescence (EL), and the like, as a light source have been proliferated. The type of illuminating fixture is provided with, for example, a lighting apparatus (an LED lighting apparatus) disclosed in Japanese Patent Application No. 2005-294063 (hereinafter referred to as a “Document 1”).
The lighting apparatus in Document 1 is a self-excited type and does not have a dimming function. It is therefore impossible to dim the light source load.
Meanwhile, International Publication Number WO 01/58218 A1 (hereinafter referred to as a “Document 2”) discloses that supply power to a light source load (an LED lighting module) is turned on and off at a burst frequency of 100 Hz or 120 Hz synchronized with a frequency (50 or 60 Hz) of an AC power supply (a main power supply voltage). The lighting apparatus (a power supply assembly) can control a length of a pulse in which the supply power to the light source load is in an On state, thereby performing a dimming control. However, a specific circuit configuration for dimming is not disclosed in Document 2.
However, as described in Document 2, in the lighting apparatus configured to perform dimming by controlling a pulse length (an On time), when a dimming ratio is small (dark), the On time in one period of the burst frequency is short, which may cause flicker. For this reason, in the lighting apparatus, a range of selectable dimming ratios is difficult to be set widely.